Support structures are required if you wish to print complex geometries such as steep overhangs or long bridges. Powder-based technologies do not require support structures, since the powder can hold the structure. Support structures are necessary when printing with filaments and resins to ensure that the printed object remains intact. The two most common materials used as supports are HIPS and PVA. We will discuss these in greater detail in this article, specifically their use in FFF.
It is difficult to select the correct support material due to their diverse requirements. The supports must be easy to remove after printing, and they should leave no traces. In the best scenario, the supports will be made of a material different from the one that was used to print the object. To reduce printing time, and the possibility of a material mix-up, it’s recommended to use a FFF with dual extruders. There are filaments that are designed or suitable for printing support. We compared PVA and HIPS based on their printing properties, characteristics and applications. PVA is used primarily as a soluble material support in FDM 3D Printing, whereas HIPS is used as both a support and a printing material. We will concentrate on its use primarily as a support material.
Complex 3D printed object with PVA support (photo credit: Zortrax).
The properties of HIPS and PVA
PVA and HIPS both are thermoplastic polymers. PVA is a thermoplastic polymer that is made by alkaline hydrolysis of polyvinyl Acetate (PVAC), which involves splitting chemical bonds by a reaction with the water. HIPS, on the other hand, is made from a mix of high impact rubber and polybutadiene. This copolymer combines the elastic properties and strength of polystyrene with rubber.
HIPS shares many of the same properties as ABS but is stronger and more resistant to impacts. HIPS is also known for its high impact strength, lightweight, resistance, and mechanical resiliency. The printed objects are smooth and resistant to scratches. They also tend to be antibacterial. HIPS is tough, but not brittle.
HIPS as an auxiliary structure (photo credit Zortrax).
Water, on the other hand, gives PVA a greater degree of elasticity and flexibility. Moisture, in general, acts as a “plasticizer” on PVA. PVA itself is brittle and fragile. Water solubility is dependent on either the composition of the PVA or the degree of saponification. The degree of hydrolysis can vary between 70 mol% and 100 mol% depending on the type of PVA. This degree affects the melting point of PVA and how quickly it dissolves. It is also very eco-friendly to dispose of PVA dissolved in water. PVA’s solubility is what makes it unsuitable for durable printing. HIPS on the other hand is a great material to use as a support.
PVA is only to be used in conjunction with materials having a similar melting temperature, like PLA, so as to avoid printing errors. The melting point is 230°C for PVA and 220°C for HIPS. The melting point for PVA, although theoretically 230 degrees is true, depends on the type. The melting point of fully hydrolyzed PVA is lower, ranging from 160 to180 degrees.
PVA, unlike HIPS dissolves readily in water (photo credit: XYZ printing)
The material can degrade even though HIPS cannot dissolve in water. It is susceptible to being broken down by chemicals, acids, organic solvents, and alkalis. Limonene, gasoline and other chemicals can cause HIPS material to decompose, become brittle or discolored. If it is used for support structures, then it must be treated with limonenes (also known as citrus peel waste) in order to decompose. As other plastics react with disintegration to acids, alkalis, and other chemicals, HIPS is not suitable as a support for other materials. It is best to print with ABS because it’s acid-resistant. PLA and PETG are not compatible. PVA should be used to support the structures when using these materials.
PVA is similar to HIPS in terms of its tensile resistance. It has a low tensile of 22MPa. PVA is not flexible but becomes more elastic with water. Both are nontoxic and odorless. Printing with HIPS, however, can cause unpleasant fumes. PVA has a natural color range from transparent to creamy, while HIPS can be purchased as a filament in white that can then be colored. The question of colouring is unnecessary in this instance, because PVA is used more as a disposable object or support material than HIPS.
PVA spool by ESUN. (Photo credit: ESUN).
3D Printing with PVA and HPS
Stores
To get the best results from 3D printing using PVA, it is important to store the filament in a cool, dry place away from light (natural or artificial), dust, and moisture. HIPS and PVA are both limited in their resistance to UV light. It is essential to ensure that the right storage conditions are maintained in order to prevent printing problems. For example, the optimum storage temperature for PVA is 15 to 25 °C.
PVA can mold, so it should never be used with moisture in the air. The finished product may warp and have bubbles or other abnormalities. PVA that has absorbed moisture must be dried prior to use. A guideline is about 8 to 12 hours at 50 to 80 °C. PVA is best stored in airtight containers to prevent this. HIPS on the other side does not absorb any moisture and doesn’t need to be dried prior to printing.
The PVA has dried on the printbed (photo credit: IGO3D).
Printing Process
In general, when printing support materials you will want to set up the print configuration so that there is no distance between the support material and the final product. The surface of the part is optimal without any segregation. As the supports are destined to dissolve once the print is complete, the adhesion of the supports to the final part during the process has no relevance.
For good adhesion, use glue or adhesive tape. This can be achieved by using a slag made from a mixture ABS/acetone. For PVA, painter’s tape is ideal.
You can use glue to help HIPS adhere better to the printbed (photo credit: Makerbot).
To achieve a good printing result with PVA, the printing plate must be preheated to 45 to 60 ºC and the extruder must be brought to a temperature of between 185 and 200 ºC. HIPS, on the other hand, requires higher temperatures: between 100 and 115 ºC for the printing plate and 230 and 245 ºC for the extruder.
PVA and HPS are not suitable for supporting the same materials. This is because the support material should have a melting temperature similar to that of the object. PVA can be used for PLA, TPLA PETG CPE, and CPE. HIPS, on the other hand, is mainly used for ABS. As mentioned above, HIPS can be used with ABS because unlike other materials, ABS does not get destroyed by D-limonene, which is used to dissolve the HIPS carrier.
It is recommended that an ooze guard be used to prevent the part from oozing and to protect the support. It is important to note that if the nozzle is heated but not in use, the filament inside can seep through and even clog up the nozzle. The heated chamber in HIPS eliminates the requirement for an ooze shield. With PVA it is best to cool down the parts, as this will help solidify the PVA faster. So, the stringing of the part is reduced. A cooling fan is not required for printing HIPS.
As mentioned earlier, printing HIPS requires high temperatures. This prevents material curling, warping, or delaminating as a result of sudden temperature changes. To protect your respiratory system, it is best to use a HEPA filter or an effective ventilation system. Printing HIPS can emit unpleasant fumes, such as styrene, which are not present in PVA.
PVA has a lower printing speed than most other materials. This is because of its fragility. Printing speeds for HIPS can range from 40-80 mm/sec. Both filaments can be printed easily if your printer is properly configured. HIPS can shrink during cooling and cause warping. If HIPS is used as a support structure, however, this effect will not be a major problem since the support will be removed.
Like ABS, HIPS also tends to warp and curl under pressure (Photo credit: Sculpteo).
Post-Processing
PVA has the advantage of being easy to post-process. The whole structure is placed in warm water and then after 1-2 hours the part is removed. As PVA is biodegradable, the water can easily be poured down the drain.
The post-processing of HIPS structures involves the use a chemical that must be handled with care, and which is relatively expensive. To ensure safety, always use a respirator mask and protective gloves. Also, break large structures off by hand in order to save money on the chemical solution.
When HIPS is being used as a supporting material, it’s best to cut out the larger pieces prior to machining the piece with limonene.
Use of HIPs and PVA in 3D printing
PVA and HPS are used in 3D-printing to form supports. But that is not all. PVA can also be used to make prototypes and molds. Meanwhile, in the design field, PVA is also used for the production of decorative models.
This is taken even further with HIPS. As already mentioned, HIPS does not dissolve in water like PVA. It is light, very impact resistant and is therefore often used in the production of toys and children’s articles. It is also frequently used in the automotive industry for the production of interior parts such as dashboards or generally in the manufacture of housings for electrical and electronic devices. Another field of application for HIPS is in packaging. Takeaway meal trays are often made of HIPS, as is packaging for cosmetics. However, it should be noted that in 3D printing, both materials primary use is as a support.
HIPS is used as a stand-alone material for packaging (photo credits: Plastics Technology)
Manufacturers and Price
PVA filament is available on the market in filaments of both 1.75 and 2.85 mm. Before buying the filament, check that the thickness matches the diameter of your 3D printer’s extruder. The price of a 500-gram spool of PVA ranges from $18 to $185, with the average price being around $50. However, prices depend on the manufacturers. Among the manufacturers of PVA filaments are Arianeplast, eSUN, FormFutura, Forward AM (BASF), Infinite Material Solutions, INNOVATEFIL, MatterHackers, Mitsubishi Chemical Corporation, Neofil3D, Polymaker, PrimaCreator, Raise3D, RS PRO, UltiMaker, XYZprinting.
HIPS is much cheaper than PVA. A spool of filament is traded at a price between $13 and 38. Well-known manufacturers are Arianeplast, eSUN, Forward AM (BASF), Intamsys, Kimya, Nanovia, Neofil3D, Raise3D, RS PRO, Smart Materials 3D, MatterHackers and Zortrax. Note that the specific composition of HIPS filaments is not always the same and pay special attention to it. This is because some contain additives that can facilitate the printing process but make it difficult to remove the support after printing.
Do you already use one of the two support materials? Do you have experience with printing PVA or HIPS? Let us know in a comment below or on our LinkedIn, Facebook, and Twitter pages! Don’t forget to sign up for our free weekly Newsletter here, the latest 3D printing news straight to your inbox! You can also find all our videos on our YouTube channel.